Method of treating electrolytic coatings on magnesium and its alloys



Patentssttne 11,1940 7 2,203,670 t 1 (UNITED STATES 1PATENT OFFICE COATINGS ON MAGNESI UM AND ITS ALLOYS Robert Remington, Md. t N cmswi Application June, 1931; e 8erialNa150,932 t w (CLZM-l) (Granted unset-f the act of Mamas, 1883, u t I t t amended Aprll-30, 1928; 370 757) t t t This t invention relates to the treatment pr As further examples of compositions which :electrolyticallyttformedcoatings on magnesium will satisfactorily seal electrolytic coatings on and its alloys in which magnesium predominates magnesium, the following are cited:

and one of its objects is to; increase the durability t t andthe protective characteristics of the film by t t P cent ,5

t t t t t t a) Dichromate 1to30 t t sealing the t t t Chromium fluoride as to The method specificallyrelates to thetreating t t j "-"7'5f'" I Hot electrolytic coatings on magnesium and l its j (1)) Sodium dichramate .s. 10 alloys withta solution in the presence of heat so Chromium fluoride...-..; ...Q i 1 10 as to form a sealthat not only increasesttthe 1 1o t. durabilitytoi the articlc coated to-wearbutalso ifg g'lf m fggg :3

improves its resistance to corrosion. t chromium fluoride 'f t The article to be treated in this manner, which '7 t 1 hasbeen' coated electrolytically, is washed free o u -eoftsolution, providing the electrolytic bath is 3 59 t 1 i5.

basically different from thesolution used my my marieslum phosphate t 1 1 sealingmethodandis then immersed in a hot C i fluoride 1 solution of sealing compounds, preferably at or t j t above the boiling point of the solution, but below a gif flfifi fj 4}:

1 the fusion point of the metal. t t Chromium sulphauh t 1 20 The sealing solution should contain acorrosion t inhibiting ion such as either a chromate 01' di- (0 m -r 1939 chromate and a second water solublesalt con-X f U taining an ion of either manganese or chromium Sodium dj hrbmate 0 i -or borate, phosphate, fluoride or a combination 1 56mm s 5 35 t of any of the said second salts. The concentration of the salts is limited only by their solubility. Dichromate; 1 to but may be varied to conform with time of apsulphate 1 0 V plication and quality of seal. Good seals of 3n coated metal have been obtained by subjecting (D t :8 m t e the coatings totreatment for periods varying enga'nous s a 1 from five minutes l30 one 1101111 (j) Ammonium dichromate 10to20 pe i ly, as n x mp aif an an ic c a Man anous sulphate; 5m 10 ling pe formed on magnesium or its alloys in a J V 7 3 bath of lll percentdichroniate and a 2per cent (19 Zinc chromatin-l; 1 monobasic phosphate and the coating has been Manganous sulphate-mu- 1 washed free of anodizing solution, its corrosion Chmmium fluoride 1 resistance will be greatly improved if it is immersed in a solution: of dichromate and man- (I) g fi gg 4n ganous sulphate at boiling temperature of water Manganous i'figgf 5 to 10 40 or above. The sealing solution may be varied p to contain a trivalent chromium salt as chromium m t 1 t 30 acetate or sulphate or fiuoride. A chromate may Fluoride 35 t 20 be introduced or substituted in the solution or a t t e phosphate may be substituted or added when the (11') Dlchlomate 10 solution is of such composition not to cause detrisodium fluoride 5 mental inter-solutionreactions. Chromium fluoride 1 It should be understood that the protection obtained by my treatment is dependent on the (0) 3:3? i i it presence of an electrolytic coating and is not a t Sp "77' e o prime surface treatment. (p) Sodium phosphate 10 In the sealing treatment herein set forth a Dichromate 10 chemical reaction is produced improving the it Chromium fluoride 1 i characteristics of the electrolytic coating. This t D1 h t t t 10 553Change is evincedby a corrosion test wherein q gfi fi' 'gaiigjg "e"' 1o two identical anodized articles one sealed by my zifihospimte p 1 method and one unsealed, disclosed over a cort rosion period that the sealed coating did not (r) Zinc chromate- 1 change in color,twhereas the unsealed coating Sodium dichromate. 5 1

t showed a radical change in color. t Chromium fiuoride A double "dip may also bie used: such as first imymersing the electrolytically coated article in a y solution of dichromate and phosphates followed by an immersion in a solution of manganese and chromium sulphatej Ammonium andother salts may'be substituted for the sodium and potassium o ter indicated broadly above and is not to be limited except by the appended claims.

The invention described herein maybe manu factured used. by or for the Government of the, K

coatings on magnesium 'oralloys thereofin which UnitedStates-oi America for governmental pur-' poses without tl epayment of any royalties ther'eon V or therefor.

V I I What I claim is:

-whicl'1 magnesium v V forming on the metal an anodic coatingpijoduc'ed 1; The method of producing corrosion resistant coatings on magnesium ormagnesium alloys in predominates comprising by reaction with magnesium and subjecting the coatingto a non-electrolytic treatment for five minutes to one hour in an aqueous solution containing 1 to -30 percent water solubledichromate and 8 to 12 percent manganous sulphate, and maintainingthe temperature of the solution during treatment substantially. equivalent to the boiling point of the solution.

'2. The method of producing corrosion resistant V coatings on magnesium .or magnesium alloys in which magnesium predominates comprising forming on the metal an'anodic coating produced by reaction with magnesium and subjecting the coating to a non-electrolytic treatment from five to sixty minutes in an aqueous solution containing 8 to 12 percent watersoluble dichromate and 8 to 12 percent water soluble'sodiumv phosphate, and maintaining the temperature of the solution during treatment substantially equivalent to the [boiling point of the solution;

I 3. The method ofvproducing corrosion resistant coatingson magnesium or alloys thereof in which -magnesium predominates comprising forming on l the metal an anodi'c coating produced by reaction 1 with magnesium, and subjecting said coating to a non-electrolytic treatment in an aqueous solution containing manganese sulphate and a water-solmentioned by way of I .uble compound selected from the group consistsuch solution being on the acid side.

4. The method of producing corrosion resist ant coatings on magnesium or alloys thereof in comprisin which 'magnesium predominates 'ing of the chromates and dichromates, the pH of I forming on the metal'an anodic coating produced by reaction with magnesium, and subjecting said I, coating to a non-electrolytic treatment in an aqueous solution containing atleast 1 per cent of a water-soluble sulphate and of a water-soluble; compound selected from the group'consisting of p the chromates and dichromates, the pH of such solution being on the'acid side. 7 v

5. The method of producing corrosion resistant magnesium predominates comprising forming on the metal an anodic coating produced by reacgroup consisting oftthe chromates' and dichro mates, the pH of such solution being on the acid side. l

6. The. method bf producl'n corrosion resistant coatings on magnesium [oralloys thereof in which magnesium predominatescomprising forming on the metal an anodic' coating produced by reaction with'magnesium, andsubjecting said coating:

to a non-electrolytic treatment in an aqueous solution containing a waterl soluble fluoride'and a water-soluble compound selected from the group consisting ;of the chromates and dichromates, the pH of such solution being on' the acid sidefl jv v 7; The method of producing corrosion resistant {coatings on magnesium or alloys thereof in which magnesium'predominates comprising forming on the metal an'anodic coating produced by reaction withfmagnesium, andfi-subj'ecting said coating to a non-electrolytic treatment in an aqueous solution containinga water-soluble phosphate and, a water-soluble. compound selected from the groupconsisting of the chromatesand dichromates, followed by, a second non-electrolytic treatment iri a solution containing manganese sulphate andchromium sulphate.

ROBERT; W BUZZARD. 

